I think it will help the searchers to identify which answer is correct and which one is wrong..! In stack overflow most of the answers are having 0 reputation, 60% question's answers are not accepted also.

I accept the down votes let me ask one more question. the down votes will indicate the answer is rejected then what is the need for

@SujithKarivelil: the accepted question points are exempt from the reputation cap, and the marker is in addition to upvoting. Also, you cannot vote up until you have 15 points at least, so for new users they have no other options.
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Martijn Pieters♦Jul 19 '14 at 13:59

okey leave it was only a suggestion from my side
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Sujith KarivelilJul 19 '14 at 14:01

@SujithKarivelil: yes, and people are voting on the suggestion; you tagged it as a feature-request, and I gave my opinion on the request (i.e. I don't think there is a need for it).
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Martijn Pieters♦Jul 19 '14 at 14:02

When it comes to accepting an answer, obviously the OP is happy - they got their solution. It's pretty hard to abuse an acceptance checkmark because you're indicating to the world "this answer solved my problem."

On the flip-side, a mark that explicitly says "this did not solve my problem" is highly prone to abuse. There are a lot of people out there whom are very stubborn, and refuse to accept answers which tell them something they simply don't want to hear, even though they are 100% correct and should be the accepted answer. Letting them put a mark on it that basically tells the world "this is stupid" is very damaging, and only allowing the OP to downvote it limits that damage greatly. It's easy for other users to upvote it if it was actually useful, but there's nothing other users can do to get that ugly mark off of it.